1. Field of the Invention
This invention relates to telecommunications systems, and more particularly to a method and apparatus for detecting and determining the point of origin of events in a telecommunications system.
2. Description of Related Art
Public Switched Telephone Networks (PSTN) commonly utilize Time Division Multiplexing (TDM) transmission systems to communicate both voice and data signals over a digital communications link. For example, DS1 (digital signal level 1) data paths are currently used to carry both voice and data signals over a single transmission facility. DS1 paths carry DS1 signals which are transmitted at a nominal rate of 1.544 Mb/s. DS1 paths reduce the number of lines required to carry voice and data signals. Data paths, such as DS1 paths, have a portion of the data transmission capability assigned to communicating customer information from one end of the data path to the other. This portion of the transmission capability is commonly referred to as the xe2x80x9cpayloadxe2x80x9d. In addition, another portion of the transmission capability is assigned to overhead functions, such as error detection and maintaining the data path. This portion of the transmission capability is commonly referred to as xe2x80x9coverheadxe2x80x9d.
DS1 facilities are used in large part to carry signals switched by components of the PSTN. However, point-to-point DS1 data links are also used to interconnect equipment controlled by different data users. A typical DS1 signal path is shown in FIG. 1. DS1 transmission systems, like the one shown in FIG. 1, include three general equipment types: (1) terminating equipment, (2) user interface equipment, and (3) transmission equipment. Terminating equipment 10 primarily serves to build the DS1 1.544 Mb/s TDM signal from the various sub-rate voice and data signals. Terminating equipment 10 typically performs Pulse Code Modulation (PCM) and TDM functions. The terminating equipment 10 also de-multiplexes the 1.544 Mb/s DS1 signal to separate voice and data signals at their original sub-rates.
The user interface equipment typically comprises a Channel Service Unit (CSU) 20 which connects the terminating equipment 10 with the transmission equipment 30, such as a DS1 path and ensures that both ends of the DS1 paths 30 send and receive a high quality DS1 signal. The CSU 20 typically checks for conformance to certain standards which are set by the telecommunications industry. The CSU 20 corrects and detects errors in the DS1 transmission path. For example, the CSU 20 corrects Bipolar Violations (BPV). In addition, the CSU 20 detects various errors and inserts alarm indications and zero substitution codes in the DS1 transmission path, including Remote Alarm Indication (RAI), Alarm Indication Signal (AIS), and Bipolar with Eight-Zero Substitution (B8ZS) signals.
The DS1 path 30 includes hardware used by the network providers to transmit DS1 digital signals between equipment controlled by different data users. The DS1 path 30 as shown in FIG. 1 is implemented by a T1 line. However, other facilities, such as coaxial cables, fiber optic cables, and microwave links may be used by providing an appropriate transport interface between the Channel Service Unit (CSU) 20 and the facility.
DS1 signals may be transmitted over a dedicated point-to-point network as simple as the one shown in FIG. 1 utilizing twisted wire pairs and repeaters spaced at intermediate points. Alternatively, the network may be as complex as the one shown in FIG. 2 which utilizes a combination of twisted wire pairs and repeaters, multiplexers, Digital Cross-connect Systems (DCS), Add Drop Multiplexers (ADM), Fiber Optic Terminals (FOT), Coaxial Cable, Microwave, Satellite, or any other transmission media capable of transporting a DS1 signal. In some instances, DS1 signals may be carried over a network similar to the point-to-point network, but having the added capability to switch the DS1 signal (in a DCS or ADM) in a manner similar to the PSTN.
While DS1 transmission systems such as the system shown in FIG. 1 are well-known, customers more typically communicate using a public DS1 network, as shown in FIG. 2. In the DS1 transmission system shown in FIG. 2, equipment is divided into categories based on the location of the equipment. Essentially, the equipment is broken into three categories: (1) the Customer Premises Equipment (CPE) 40; (2) the Local Exchange Carrier (LEC) equipment, which comprises the local loop 42 and the central office equipment; and (3) the InterExchange Carrier (IEC) 52. CPE 40 belongs to the network user (or customer). The customer that owns the CPE 40 is responsible for both its operation and maintenance. The customer must ensure that its equipment provides a healthy and standard DS1 digital signal to the local exchange carrier equipment 42. The equipment 40 on the customer premises typically consists of DS1 multiplexers 46, digital Private Branch Exchanges (PBXs), and any other DS1 terminating equipment which connects to a CSU 20 at the CPE site. The local exchange carrier equipment 42 connects the CPE 40 with the central office 44 and the IEC 52. LECs assume responsibility for maintaining equipment at the line of demarcation between the CPE 40 and the local loop 42.
As shown in FIG. 2, a Network Interface Unit (NIU) 50 may be coupled between the CPE 40 and the LEC equipment 42. The NIU 50 represents the point of demarcation between the CPE 40 and the LEC equipment 42 (which comprises local loop equipment 42, and Central Office (CO) equipment 44). Prior art NIUs may be relatively simple devices which allow network technicians to minimally test the operation and performance of both the CPE 40 and the DS1 network 52 or they may be more sophisticated devices.
The CO equipment 44 may include equipment that can monitor for various DS1 signal requirements. Independent of whether the DS1 transmission system is simple (FIG. 1), complex (FIG. 2), or switched, all the circuits and network equipment required to transmit a DS1 signal must be tested and maintained to operate at maximum efficiency. In order to perform such test and maintenance functions, equipment within the DS1 path provides maintenance signals indicative of particular conditions on the incoming and outgoing signals. These signals are defined by standards established by the American National Standards Institute for operation of DS1 communications links (ANSI T1.403 and ANSI T1.408, et. al). These indications include (1) RAI, which indicates that the signal that was received by the CPE equipment from the NIU 50 was lost (the detailed requirements for sending RAI are contained in ANSI T1.231); and (2) AIS, which is an unframed, all-ones signal which is transmitted to the network interface upon loss, or in response to the presence of a signal defect of the originating signal, or when any action is taken that would cause a service disruption (such as loopback). In addition, detection of signal defects in the digital hierarchy above DS1 shall cause an AIS signal to be generated. The AIS signal is removed when the condition that triggered the AIS is terminated.
In addition to these indications, ANSI T1.403-1995 defines a performance report message (PRM) which is sent each second using a format which is detailed in the standard. PRMs contain performance information within a xe2x80x9cmessage fieldxe2x80x9d portion of the PRM for each of four previous one-second intervals. Counts of cyclic redundancy checking (CRC) errors are accumulated in each contiguous one-second interval by the reporting equipment. For example, a one bit (designated xe2x80x9cG1xe2x80x9d by the ANSI standard) within the variable portion of the PRM indicates that one CRC error had occurred within the last second of transmission. At the end of each one-second interval, a modulo-4 counter within the variable portion of the PRM is incremented, and the appropriate performance bits are set within the remainder of the variable portion of the report in accordance with the PRM format provided in the specification. Other bits indicate that: (1) between 2 and 5 CRC events had occurred; (2) between 6 and 10 CRC events had occurred; (3) between 11 and 100 CRC events had occurred; (4) between 101 and 319 CRC events had occurred; (5) greater than 319 CRC events had occurred; (6) at least one severely errored framing event had occurred; (7) at least one frame synchronization bit error event had occurred; (8) at least one line code violation event had occurred; and (9) at least one slip event had occurred. The number and type of Events indicates the quality of transmission. Each Event is defined within ANSI T1.403.
Performance reports may be also be generated and transmitted in accordance with ATandT PUB 54016 Performance Reporting. PRMs are only transmitted by equipment that conforms to the Extended Superframe Format (ESF) described in ANSI T1.403. PRMs provide information that can be used in xe2x80x9cSectionalizationxe2x80x9d of the DS1 path. Sectionalization is a process by which several sections of a data path are analyzed to determine in which section a communication problem originates. In particular, for the purposes of this discussion, sectionalization refers to determining whether a problem in the DS1 path originates within the CPE equipment 40 (for which the customer is responsible), the LEC equipment 42, 44 (for which the local exchange carrier is responsible) or the T1 network equipment 52 (for which the Intermediate Exchange Carrier (IEC) is responsible).
Currently, when a problem is reported on a DS1 path, sectionalization of the path is performed by sending a technician to several points along the path to collect data. The collected data is then reviewed by the technician in an attempt to determine the point of origin of a problem. Since the equipment that makes up the path is physically distributed over a large geographic region (equipment at one end of the path may be thousands of miles from equipment at the other end of the path) it is typical for several technicians to become involved in the sectionalization of the path. Each technician must be highly skilled and trained in order to collect the data from the various points along the path. In some cases, the revenue bearing signals being transmitted over the path must be disrupted in order to perform tests which generate data to be collected or in order to collect data that is developed in real time during the transmission of the revenue generating signals. In many cases the responsibility for sectionalizing the DS1 path must be shared by the LEC, IEC, and customer, since each party is responsible for maintaining a portion of the equipment that makes up the path. Accordingly, each party incurs an expense when equipment maintained by any of the other parties experiences a problem.
Furthermore, out-of-service testing causes xe2x80x9clivexe2x80x9d traffic to be removed from the DS1 link before testing commences. In out-of-service testing, a test instrument transmits a specific data pattern to a receiving test instrument that anticipates the sequence of the pattern being sent. Any deviation from the anticipated pattern is counted as an error by the receiving test instrument. Out-of-service testing can be conducted on a xe2x80x9cpoint-to-pointxe2x80x9d basis or by creating a xe2x80x9cloop-backxe2x80x9d. Point-to-point testing requires two test instruments (a first instrument at one end of the DS1 transmission system, and a second instrument at the other end of the DS1 transmission system). By simultaneously generating a test data pattern and analyzing the received data for errors, the test instruments can analyze the performance of a DS1 link in both directions.
Loop-back testing is often used as a xe2x80x9cquick checkxe2x80x9d of circuit performance or when attempting to isolate faulty equipment. In loop-back testing, a single test instrument sends a xe2x80x9cloop-upxe2x80x9d code to a loop back device, such as the CSU at the far end, before data is actually transmitted. The loop-up code causes all transmitted data to be looped back by the CSU in the direction toward the test instrument. By analyzing the received data for errors, the test instrument measures the performance of the link up to and including the far end CSU. Because loop-back testing only requires a single test instrument, and thus, only one operator, it is a convenient testing means.
Both point-to-point and loop-back tests allow detailed measurements of any DS1 transmission system. However, because both testing methods require that live, revenue-generating traffic be interrupted, they are undesirable. Thus, out-of-service testing is inherently expensive and undesirable. It is therefore desirable to perform in-service monitoring of xe2x80x9clivexe2x80x9d data to measure the performance and viability of DS1 transmission systems. Because in-service monitoring does not disrupt the transmission of live, revenue-generating traffic, it is suitable for routine maintenance and it is preferred by both the LECs and their customers.
Referring again to FIG. 2, the prior art NIUs 50 disadvantageously provide only intrusive test and performance monitoring functionality. End-user customers object to the service interruptions and disruptions required by the out-of-service testing performed by the prior art NIUs 50. The LECs install the NIUs 50 at the demarcation point between the CPE 40 and the LEC portions of the network (i.e., at the interface to the local loop 42). The prior art NIUs 50 typically have provided the LECs with a loop-back point for testing DS1 digital circuits to the network boundary. Disadvantageously, customer circuits may be taken out-of-service for intrusive testing only with customer permission. Customers typically do not authorize such intrusive testing means unless a circuit is completely unusable.
There are several types of NIUs 50 currently in use. One of the most popular types of NIUs 50 is the xe2x80x9cSmart Jackxe2x80x9d available from Westell, Inc., located in Oakbrook, Ill. The Smart Jack NIU with Performance Monitoring (PM) allows the LECs to determine what errors are received and generated by the CPE 40. A major disadvantage of the Smart Jack NIU is that the NIU accumulates PM data and stores the data in a local buffer for later retrieval by LEC personnel. Data retrieval in most areas requires that a circuit be taken completely out-of-service and that the NIU be commanded intrusively using a proprietary command set. Furthermore, the Smart Jack NIU disadvantageously provides no practical method for the LECs to retrieve the performance monitor data collected by the Smart Jack NIU. While the Smart Jack NIU does allow non-intrusive transmission of PM data from the Smart Jack to the central office, a paralleling maintenance line must be provided. Most DS1 installations to customer premises, however, do not provide such maintenance lines.
Other NIUs 50 are available from Wescom Integrated Network Systems (WINS), the Larus Corporation, and Teltrend, Inc. All of the prior art NIUs 50 suffer the disadvantages associated with out-of-service monitoring and testing. Therefore, there is a need for an improved NIU 50 which provides non-intrusive maintenance performance monitoring at the point of demarcation between the CPE 40 and the LEC equipment.
In addition to being unable to provide non-intrusive monitoring of DS1 digital equipment, the prior art NIUs 50 are unable to provide an indication of a loss of signal (LOS) caused by the CPE 40 which is distinguishable from LOSs that are caused by failure of the network equipment. Currently, LOS caused by the CPE 40 generates alarms in the LEC central office equipment 44 which are indistinguishable from the alarms generated in response to LOSs caused by equipment failures in the local loop 42, Central Office 44, or DS1 network 52. Therefore, there is a need for an improved NIU which allows the LECs to distinguish LOS alarm signals caused by loss of signal within the CPE 40 from alarms which originate due to loss of signal within the LEC or network. With such an improved NIU, the LECs can then decide whether to notify their customers of the LOS indication or to ignore the indication as they deem appropriate.
In addition to these disadvantages, the prior art NIUs 50 do not permit the LECs to control the frame format of data transmitted by their customers and transmitted over the LECs"" networks. In general, DS1 signals can be transmitted to the local loop 42 using four basic DS1 frame formats: (1) Super Frame format (SF); (2) Extended Superframe Format (ESF) without Performance Report Messages (PRMs); (3) ESF with ATandT PUB 54016 Performance Reporting; and (4) ESF with ANSI T1.403 Performance Report Messages (PRMs). Most DS1 signals are transmitted using the SF format, and the remainder are transmitted by the CPE 40 using a mix of ESF format types. Performance monitoring capabilities of the various formats range from poor in the case of SF (most of the data is not monitored), to excellent, in the case of ESF with ANSI T1.403 PRMs. The difficulty faced by the LECs is that their ability to monitor data and transmission performance is tied to the frame format used by the CPE 40. Because the customer is responsible for the CPE 40, the LECs are unable to control the frame format used and thus the level and extent of performance monitoring and testing that is achievable. The present invention allows the LECs to control the frame format of data by converting the frame format transmitted by the CPE 40.
The ESF format has long been recognized as the single most important change occurring in the telephone network with respect to the quality of service provided on DS1 circuits because it addresses the above-stated need for non-intrusive monitor and test capability. ESF allows customers to continuously and non-intrusively monitor the performance of their DS1 facilities while the applications remain active and thus income-generating. ESF performance monitoring provides both a precise performance report and a proactive maintenance tool. With ESF performance data, a customer can determine correlations between data application performance (response time) and errors which occur on the DS1 facilities. This can aid in troubleshooting end-user response time problems. By looking at the error conditions, the cause of the increased response time can be determined and the appropriate action can be taken.
In addition, the ESF frame format offers the network providers the ability to xe2x80x9csectionalizexe2x80x9d problems occurring in the network. By placing ESF monitoring equipment throughout the network, an LEC can monitor the various facilities that make up an end-to-end customer circuit. When customers complain about a degraded or unavailable circuit, the LEC can use the ESF format to locate the faulty link in a real time, non-intrusive manner.
Although the ESF frame format has long been recognized as a tremendous benefit, it has gained little acceptance and use in the CPE 40. Therefore, there is a need for an improved NIU which allows telephone companies to add the ESF functionality to existing DS1 circuits. There is also a need for an improved NIU which will provide telephone companies an adaptive way to increase the number of circuits that use the preferred ESF signal format as the circuit enters the LEC equipment. Moreover, there is a need to combine the functions of network interface, circuit loop-back, frame format conversion, CPE loss of signal detection, and signal degradation detection functionality together in an inexpensive and easily accessible NIU. The present invention provides such an improved NIU.
In addition to the problems which arise due to the inability of CSUs to use ESF frame formatting, it is currently difficult to collect at the Operations System (OS) a sufficient amount of data unobtrusively in real-time to allow automated sectionalization of a data path. Current systems provide for monitoring each data path at the CPP and storing information in the monitoring device until a request is made to communicate the information stored to the OS. However, due to the large amount of information which must be stored, the data is stored in a manner which does not allow the time at which an event occurs to be known with better than a 15 minute resolution. Accordingly, if more than two Events occur in the same 15 minute interval, the ability to distinguish one event from the other is lost. Furthermore, unless there is a reason to suspect a problem on a particular data path, the data is not requested. Still further, in prior art data paths in which data is collected and transmitted at regular intervals (such as by PRMs generated by a CSU) this data is not collected at the network interface, and therefore the ability to sectionalize the data path does not correlate with the portions of the data path which different organizations are responsible for maintaining.
Accordingly, it would be desirable to provide a system which sectionalizes a DS1 path to allow each of the parties responsible for maintaining equipment along the path to determine which party is responsible for the problem. Furthermore, it would be desirable to reduce the cost of sectionalizing a DS1 path by determining the location of the origin of the problem without sending a highly skilled technician to a plurality of locations along the path. Still further, it would be desirable to provide such a system which is capable of sectionalizing a DS1 path in xe2x80x9creal-timexe2x80x9d without disrupting revenue bearing signals transmitted over the path. The present invention provides such a system.
The present invention is an improved network interface unit having an adaptive DS1 frame format conversion device (hereinafter referred to as the xe2x80x9cRemote Modulexe2x80x9d) which is used for remotely monitoring the performance of DS1 telephone circuits. The Remote Module is an improved network interface unit which is preferably installed on the network side of an interface between customer premises equipment (CPE) and equipment provided by the network provider. The Remote Module is used to non-intrusively collect and transmit full-time performance monitoring data to the network provider. The Remote Module provides continuous and non-intrusive performance monitoring of DS1 transmission systems. With the Remote Module installed at the interface between the customer""s CPE and the LECs"" equipment, network service providers are alerted to potential problems before they adversely affect the service provided to their customers. The Remote Module enables a network service provider to quickly and non-intrusively determine whether a problem exists in the equipment provided by the network provider or in the equipment on the customer""s premises. The Remote Module, therefore, advantageously eliminates false dispatches and expensive and unnecessary troubleshooting required in systems which use prior art network interface units.
The Remote Module provides non-intrusive testing and monitoring of CPE by facilitating the conversion of CPE-generated signal frame formats to the Extended Superframe Format (ESF) (according to the ANSI T1.403 Standard with Performance Report Message). The present invention performs an adaptive real-time DS1 circuit frame format conversion. The present invention preferably accommodates all DS1 frame formats commonly used in customer premises applications. For example, if the CPE uses an ESF-formatted signal having a maintenance channel using an ANSI T1.403 standard ESF PRM signal, the present invention concatenates additional performance monitoring data, gathered by the Remote Module, onto the CPE-generated signal. In this case, the additional performance monitoring data is xe2x80x9cpiggy-backedxe2x80x9d onto the customer-generated performance report messages. Alternatively, if the customer""s DS1 circuit is ESF-formatted, but the ESF Data Link (DL), defined by ANSI T1.403-1995 clause 9.4, is not in use, the DL is used to transport the additional performance monitoring data, and no frame format conversion is performed by the Remote Module. If the customer""s DS1 circuit is ESF-formatted and is carrying ATandT PUB 54016 poll and response data, the present Remote Module inserts the ANSI PRMs into the maintenance channel, carefully observing a protocol that will avoid interference with the ATandT maintenance channel commands and responses. The present invention preferably passes unframed signals without modification.
The Remote Module of the present invention is an electronic circuit which combines the network interface, with the NI circuit loop-back, frame format conversion, CPE loss-of-signal detection, and signal degradation monitoring functions together into an inexpensive and compact device. The present invention operates transparently to the CPE. The signals generated by the CPE are returned to their original format before being transmitted to the customer. The CPE, therefore, has no access to the ESF-formatted signals if the ESF signals are not provided by the CPE. Importantly, the Remote Module provides a network loopback function as defined in ANSI T1.403 which carefully avoids superseding or tampering with the CPE loopback functionality. This is important to avoid disrupting the ability of end users to locate trouble in their own DS1 networks.
In addition to accommodating all commonly used DS1 frame formats, the present invention preferably provides an indication of Loss of Signal caused by the CPE which is distinguishable from the LOS signals caused by a failure of equipment provided by the network provider. Upon detection of a Loss of Signal from the network equipment, the Remote Module, similar to the prior art NIUs, sends an Alarm Indication Signal (AIS) to the CPE. However, upon detection of an LOS from the CPE, the present invention preferably transmits a unique code to the network equipment which indicates that the LOS originated from the customer side of the network interface (AIS-CI). The unique code is read as an AIS by elements located in the DS1 transmission system which are not specially equipped to read AIS-CI. AIS and AIS-CI are special signals which suppress downstream LOS indications while, at the same time, alerting surveillance points to the existence of an upstream LOS or other qualifying condition and ensuring proper ones density in the network.
Furthermore, the present invention preferably provides an indication of LOS on the signal received by the CPE which is capable of indicating whether the LOS occurred prior to the signal being received by the Remote Module or between the time the signal is transmitted from the Remote Module and received by the CSU. That is, the present invention is capable of modifying a Remote Alarm Indication (RAI) received from the CSU if the Remote Module received a signal from the network which was not in alarm condition. This modified signal is referred to as an RAI-CI signal.
The present invention includes an auto-provisioning function which facilitates the deployment of multiple Remote Modules. A Remote Module in accordance with the present invention auto-provisions to a frame format conversion mode of operation when it detects the presence of a second Remote Module positioned at a distant end of the DS1 transmission system. The auto-provisioning function allows Remote Modules which are installed subsequent to the installation of other Remote Modules in a DS1 transmission system to begin proper operation without requiring additional expensive site visits by network provider employees. Frame format conversion and other features provided by the present invention are remotely provisionable via an ESF DL. In addition, performance monitoring data is transmitted periodically (i.e., in the preferred embodiment once per second) over the DL, and such data can be non-intrusively accessed at a distant point within the DS1 path.
The present invention also provides a method and apparatus for automated sectionalization of xe2x80x9cEventsxe2x80x9d in a DS1/DS3 data path based upon information received by a single device along the data path. Events are preferably defined as performance primitives and parameters defined in ANSI T1.231 at paragraph 6, et seq. However, in accordance with an alternative embodiment of the present invention, Events may be defined as a subset or super set of these primitives and parameters. The information is processed in order to determine the point of origin of problems detected on the path.
More particularly, a test and monitor device is located at a point of demarcation between a Local Exchange Carrier (LEC) and an Intermediate Exchange Carrier (IEC). In addition, in the preferred DS1/DS3 data path configuration, a Remote Module is located at a point of demarcation between the LEC and the Customer Premises Equipment (CPE). The test and monitor device receives the following information indicating the occurrence of an Event:
(1) Alarm Indication Signals (AISs);
(2) Alarm Indication Signal-Customer Installation (AIS-CI);
(3) Remote Alarm Indications (RAIs);
(4) Remote Alarm Indications-Customer Installation (RAI-CI);
(5) Performance Report Messages (PRMs) (if the received signal is in Extended Superframe Format (ESF) with PRMs); and
(6) Supplementary Performance Report Messages (SPRMs), (if a Remote Module is present in the path between the CPE and the test and monitoring equipment).
In addition, the test and monitor device of the preferred embodiment of the present invention is fully ANSI compatible (i.e., is capable of monitoring each of the performance primatives and parameters defined by ANSI T1.231 paragraph 6, et seq.). The present invention processes this information in order to determine the point of origin of any Event, such as an xe2x80x9cErrored Secondxe2x80x9d or an alarm which is detected at the test and monitor device. In an alternative embodiment of the present invention, any subset or super set of these parameters and primatives may be monitored by the test and monitor device.
The information that is received is processed in a three step process in order to generate a xe2x80x9cSectionalizer Reportxe2x80x9d. The Sectionalizer Report can be output as a graphical display on a video output device (such as a video monitor), or the data can be transmitted to a remote device, such as an Operations System (OS) over an asynchronous or X.25 communication channel. The Sectionalizer Report can be structured in accordance with one of three modes (xe2x80x9cFiltered Modexe2x80x9d, xe2x80x9cHistory Modexe2x80x9d, and xe2x80x9cCurrent Modexe2x80x9d) and two views (xe2x80x9cData Viewxe2x80x9d and xe2x80x9cSectionalized Viewxe2x80x9d).
In the first step in preparing the Sectionalizer Report, a first filter captures changes in the status of each leg in the path (as determined by the occurrence of an Event). Indications that an Event has occurred are derived from the information received by the test and monitor device (xe2x80x9cRaw Dataxe2x80x9d), and are output from the first filter only after a first predetermined period of time has elapsed or upon detection of a more severe Event. Each detected Event is held within the first filter for a second predetermined period which is longer than the first predetermined period. Accordingly, any Event that occurs will be output from the first filter before the indication of that Event is cleared. If more than one Event is detected on a particular leg in the path, then the most severe Event is output from the first filter after the first period of time has elapsed, the first period of time beginning at the time the most severe Event was detected. If the Event is no longer being detected after the second period of time has elapsed, then the Event is cleared and will not be reported in subsequent reports.
In a second step in preparing the Sectionalizer Report, a second filter xe2x80x9csmoothsxe2x80x9d changes in the status of each leg in the path. That is, the second filter imposes a delay before indications of Events in each leg of the path, unless the severity of the Event is decreased. By imposing such a delay, the output is stabilized and Events that are reported at different times from different devices due to lack of synchronization between the time reports are generated by different devices in the data path and reported in a manner which ensures that such Events are not processed as two separate Events.
In a third step in preparing the Sectionalizer Report, the information output from the second filter is used to determine where particular Events originated. Signals transmitted in each direction (i.e., to the network and from the network) are handled independently. However, if the signal reporting an Event on the signal from the network (i.e., an RAI signal) disrupts the signal being transmitted to the network (such as occurs in some instances in signals formatted in accordance with SF format), then the ability to detect Events on the signal to the network is limited. By implementing a sectionalizing method in which conditions are noted which, if present, are clear indications that a particular section of the data path is responsible for an Event, the possibilities are narrowed such that a determination can be made as to which section the Event originated within.
Operation of the sectionalizer function of the present invention may be enhanced by use of network interface units located at the point of demarcation between the LEC and the CPE which provide additional diagnostic information to the test and monitor equipment, However, such network interface units are not necessary.
The details of the preferred embodiment of the present invention are set forth in the accompanying drawings and the description below. Once the details of the invention are known, numerous additional innovations and changes will become obvious to one skilled in the art.